By some estimates, over half a million Americans took to the streets last Wednesday to protest taxes and Washington spending – the largest single-day turnout of protesters in the US since 750,000 people marched in Los Angeles in support of rights and protections for immigrants on March 25, 2006. [Editor's note: The original version misstated the purpose of the march in Los Angeles on March 25, 2006.]

Pitched as a non-partisan protest, but dominated by conservatives and libertarians, the national Tea Party protests took place in over 800 locales – from mega-city Atlanta to little Craig, Colo. – with people waving mostly homemade signs, chanting "USA! USA!" and recalling the spirit of the country's revolutionary roots to demand smaller, more responsible and more constitutional government.

Critics doubt the higher estimates of the turnout, and say the numbers represent the extreme right rather than a burgeoning political counterpoint to President Obama and current Washington policies.

Yet the idea of non-traditional protesters using bottom-up organizing to foment a national movement in the span of 60 days may have marked a turning point for the tea partiers – especially since the high attendance estimates rivaled the estimated 500,000 or so protesters who converged on New York City and several other major cities to oppose the Iraq War on Feb. 15, 2003.

"I think it's not dissimilar from what we had in 2003 with the anti-war protests, where a lot of people were uncomfortable with the war, but also uncomfortable with the anti-war position, recognizing there are terrorists out there," says Jeremi Suri, a history professor who specializes in social movements at the University of Wisconsin in Madison. "Here we have a similar thing: There are serious economic issues, and it's unclear to many people whether the stimulus is going to deal with these."

Trying to estimate crowds at over 800 rallies nationwide is, to be sure, more art than science. And experts say the counting itself often becomes politicized as authorities, organizers, and attendees often come up with dramatically different counts. Cheerleading by Fox News and the appearance of popular host Sean Hannity at the Atlanta event effected the outcome, some critics say.

The conservative Pajamas TV network said on Saturday that it used 850 citizen reporters, police accounts, and video tape to estimate the size of the crowd at each event. The network said in a release that total attendance reached 618,000.

Statistics blogger Nate Silver, who trumped many organizations with his polling data during last year's election, pegged the turnout at 240,000. But that count included only about half the locations. The largest events drew close to 20,000 people, but some drew only dozens. A protest in Washington included about 1,500 people in a heavy rain.

In comparison, the biggest of the Vietnam era protests took place on Oct. 15, 1969, and brought out several million Americans in big cities and small towns across the country. Detailed photographic analysis of the crowd indicated that about 800,000 people participated in the Million Man March on Washington on Oct. 16, 1995.

Yet organizers said this week's protests were different, not just in the profile of the protesters – older, mostly white, and libertarian versus the young, more diverse, and liberal stereotype of the average activist – but in their message and geographical breadth.

"The role of the protester has not been to fix things, but to complain about what's going on, and that's where these tea party protests are different from the average protest," says J.M. Kata, a Tea Party attendee in South Bend, Ind. "We want these problems to be fixed, and we know how to fix them: be responsible in the way you levy taxes and be responsible in how you mortgage our children's futures. Those aren't the cries of a lunatic or the criminal insane, those are common-sense everyday values held by Americans in this country."

Critics of the movement said the numbers aren't really that impressive, especially given the air time given to the topic by, among other conservative organizations, Fox News, which seemed at times to be promoting the events more than covering them.

On the other hand, the backlash against Washington's bailouts and stimulus bills targeted by the Tea Party crowd has also not been the subject of the kind of intense, nightly news that surrounded the immigration debate in 2006 and the run-up to the Iraq War, coverage which certainly fueled those protests.

Jeffrey Kimball, a professor emeritus of history at Miami University in Oxford, Ohio, says the protesters seemed to represent the most extreme adherents of American conservatism, hardly representative of the average American.

"We may have just seen the whole movement" at these protests, says Mr. Kimball. "I don't see it as a groundswell, but a manifestation by those people who form the core of ... the extreme right reacting both to the condition of our time and President Obama – he's black and he's liberal."

Whether the final tally represents a victory or defeat for the Tea Party movement will be determined by where the idea goes from here, and to what extent it can shape this year's budget debate and next year's congressional elections. More protests are planned for the Fourth of July weekend.

But the more fascinating part, says Mr. Suri, is not whether the protesters represent the tip of an iceberg, but that the sizable numbers indicate that the American right is regaining a foothold on the public debate over America's economic future.

"I think these protests are part of a larger politicization of American society, in a good way," says Suri. "People are feeling more engaged in the process, they're voicing their opinions and feeling that it matters. This is democracy in action, and those on the right have learned something from the Obama movement in that sense."